Field of the Invention
Aspects of the present disclosure generally relate to a sheet conveyance device which sequentially conveys sheets, an image forming apparatus, such as a copying machine, a printer, and a facsimile apparatus, which is equipped with the sheet conveyance device, and an image reading apparatus.
Description of the Related Art
In recent years, image forming apparatuses have been expected to cope with further resource saving, so that the use of two-sided printing (duplex printing) has become widespread with respect to sheets, such as paper, overhead projector (OHP) sheets, plastic sheets, and cloth. Therefore, in image forming apparatuses having a two-sided printing function, importance is put on increasing the number of output sheets of two-sided printing per unit time, in other words, improving two-sided printing productivity.
Japanese Patent Application Laid-Open No. 2015-083353, which serves as related art, discusses a configuration in which a reversing portion which reverses sheets is provided with a reversing roller group including one driving roller which receives driving force to rotate only in one direction, a first driven roller, and a second driven roller. In this configuration of the reversing roller group, the three rollers are aligned approximately in a straight line in the order of the first driven roller, the driving roller, and the second driven roller regarding a direction intersecting with the sheet conveyance direction. The first driven roller is located opposite the driving roller to form a first nip portion, and the second driven roller is located opposite the driving roller in a direction different from that of the first driven roller to form a second nip portion.
In the reversing portion discussed in Japanese Patent Application Laid-Open No. 2015-083353, reversal of a sheet is performed as follows. First, a sheet having an image formed on a first surface thereof is conveyed toward the first nip portion of the reversing roller group. After that, the sheet is conveyed at the first nip portion in a first direction, which is a direction to discharge the sheet from the reversing roller group, and the trailing edge of the sheet regarding the sheet conveyance direction passes through the first nip portion. The reversing portion is provided with a switchback portion, which temporarily contains a sheet, at the downstream side of the first nip portion regarding the sheet conveyance direction, and the sheet having passed through the first nip portion is contained in the switchback portion. After that, the sheet having been temporarily contained in the switchback portion falls by its own weight, so that the trailing edge of the sheet is guided to the second nip portion of the reversing roller group. Since the driving roller is rotating only in one direction, the sheet nipped by the second nip portion is conveyed in a second direction, which is a direction opposite to the first direction, which is the conveyance direction in the first nip portion. After that, the sheet is re-conveyed to an image forming portion, and, after an image is formed on a second surface of the sheet, the sheet is conveyed to a sheet discharge portion, which is provided at a position different from that of the reversing portion. Then, the sheet is discharged from inside the image forming apparatus by a sheet discharge roller of the sheet discharge portion.
More specifically, in the configuration discussed in Japanese Patent Application Laid-Open No. 2015-083353, the sheet is completely discharged from the reversing roller group to the switchback portion and is temporarily contained in the switchback portion, and a nip portion by which the sheet is nipped is switched from the first nip portion to the second nip portion. With this configuration, when two-sided printing is continuously performed on a plurality of sheets, during a period in which the first sheet passes through the first nip portion and is contained in the switchback portion, the second sheet, which is a subsequent sheet, can be conveyed to the first nip portion.
However, in the configuration discussed in Japanese Patent Application Laid-Open No. 2015-083353, in which reversal of a sheet is performed with the sheet completely discharged from the first nip portion of the reversing roller group, the downstream side of the reversing roller group regarding the sheet conveyance direction is required to be provided with a switchback portion which temporarily contains a sheet. In a case where the switchback portion is provided, since a sheet discharged from the reversing roller group is inevitably contained in the switchback portion, a sheet discharge portion, which discharges a sheet from inside the image forming apparatus, is required to be provided at a position different from that of the reversing portion, which reverses a sheet. This causes an issue that the apparatus may be increased in size.